Because valve seats mounted to cylinder heads in an internal combustion engine are repeatedly struck by valves in a high-temperature environment, various improvements have been made to improve their wear resistance, heat resistance, etc. Particularly in high-power, high-load diesel engines, a load tends to become increasingly higher on valve seats coming into contact with metal members, because of improvement in combustion efficiency for environmental protection. Accordingly, higher wear resistance than ever is required for valve seats at wider use temperatures. For diesel engine valve seats, for example, JP 61-19762 A discloses a wear-resistant sintered alloy capable of withstanding a thermal and mechanical load and having enough wear resistance, wherein titanium nitride particles are dispersed in a matrix in an area ratio of 2-30% to the matrix excluding pores; the matrix comprising by weight 1.0-3.0% of C, 0.2-1.0% of Si, 5.0-20% of Cr, 0.5-2.0% of Mo, 0.3-3.0% of V, and 0.02-0.5% in total of one or more of B, P and S, the balance being substantially Fe.
However, because TiN does not have high adhesion to the matrix, TiN dispersed in the matrix is easily detached, providing the alloy with poor machinability, thereby making it extremely difficult to machine the alloy. As a result, it is practically an expensive material. In addition, because it has relatively strong attackability to a mating body, it wears valves. Thus, diesel engine valve seats are required to have good machinability as well as improved wear resistance including so-called mating body attackability.